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Amorphous-Nanocrystalline powders of Ni79.3W20.7 and Ni55.1W17.9B27 were prepared by mechanically alloyed method. The microstructure characteristics and structure parameters of powders for different milling times were studied by SEM and XRD, respectively, and the effect of B additive on the progress of amorphization was analyzed. The research results showed that, during MA, the Ni79.3W20.7 was not amorphized, while the Ni55.1W17.9B27 was amorphized after 80 hours. It suggested that the addition of B improved the glass-forming ability of the Ni-W alloy systems. The amorphization progress was that W/B first dissolved in Ni to form Ni(W, B) supersaturated solid solution during MA, and then amorphization of Ni(W, B) supersaturated solid solution occurred. Furthermore, grain size and internal strain of Ni in Ni79.3W20.7 powder were 32.9nm and 0.48 pct after 30 hours of milling, whereas those of Ni55.1W17.9B27 powder were 9nm and 0.62 pct after 10 hours of milling.